In ad hoc networks, nodes engage in peer-to-peer communication without a set infrastructure and without coordination or oversight by a central authority such as an Access Point (AP). Mobile Ad Hoc Networks (MANETs) represent a specific type of ad hoc network in which the nodes are mobile. MANETs are commonly used for tactical military communications, communication for disaster relief, and communication among mobile sensors. Due to node mobility and the limited reach of the nodes, transmissions between a source and a destination in a MANET often must be via multiple intermediate nodes. In these scenarios, the nodes normally behave cooperatively for the overall integrity of the network.
However, not all intermediate nodes can be expected to behave reliably at all times. Their misbehavior could be due to their: (a) having limited resources (e.g., power) and thus being selfish to conserve resources, (b) having sustained a permanent or transient fault condition, or (c) being malicious.
A number of studies have dealt with the vulnerability of wireless networks and the concepts of “reputation” and “trust” have been used to model and improve their reliability. Reputation is the opinion of one entity (e.g., a node) about another. Trust, on the other hand, is the expectation of one entity about the actions of another.
There are several approaches to establishing trust and reputation models in wireless networks. One example is a distributed approach that establishes reputation-based trust among nodes in order to identify malfunctioning and/or malicious nodes. It has also been demonstrated through analysis and simulation that the packet-dropping behavior of a node (i.e., its reputation) is revealed through nearest neighbor attribution assessments in a wide variety of scenarios assuming enough node mobility in the MANET. In other words, whenever a packet fails to reach its destination in a multi-hop MANET, the failure or misbehavior can be attributed to the source's nearest neighbor on the path from the source to the destination. Assuming enough node mobility in the MANET, each node is able to determine and continuously update its view of the reputation of every other node in the MANET.
Having a trust or reputation model allows for devising routing schemes to improve security and reliability of MANETs. Examples have described a trust model based routing protocol to improve security of MANETs. One such a protocol, called Trusted AODV (TAODV), improves system performance mainly by verifying trust certificates at every routing step. In such a scheme, a node which behaves maliciously may eventually be detected and denied access to the resources of the network. Another extends Dynamic Source Routing protocol (DSR) making it possible to detect and isolate misbehaving nodes, and thus making it unattractive to deny cooperation. A further scheme identifies benign and malicious behaviors of nodes capturing evidence from direct interaction with neighbors. It then applies this evidence of “trust” to enhance the security of communications depending on decision policies, such as whether to send a packet to or forward a packet on behalf of other nodes.